Coseismic displacements and Holocene slip rates for two active thrust faults at the mountain front of the Andean Precordillera (∼33°S)
Coseismic displacements and Holocene slip rates for two active thrust faults at the mountain front of the Andean Precordillera (∼33°S)
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DOI：
10.1029/2011tc002932
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发表时间：
2011-10
期刊：
影响因子：
4.2
通讯作者：
Silke R. Schmidt;R. Hetzel;F. Mingorance;V. Ramos
中科院分区：
文献类型：
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作者：
Silke R. Schmidt;R. Hetzel;F. Mingorance;V. Ramos
在过去的几百年里，安第斯山脉前山脉东缘沿着发生了几次破坏性地震，GPS数据显示那里的缩短速率为1.45 mm/a。我们使用断层崖剖面和变形阶地（T1-T4）的年龄测定来推断同震位移，并量化门多萨市附近的佩尼亚斯和卡尔逆冲断层的滑动速率。最低阶地水平T1上的陡坎揭示了两个断层0.8-1.0 m的垂直偏移，这被解释为上一次地震期间的同震位移。与断层倾角一起，这些偏移表明这两个断层都能够产生MW ≥ 6.9级地震，这被1861年摧毁门多萨的Cal断层上的MS = 7.0级事件所证实。在Peñas逆冲断层处，阶地T2的年龄为3.3 ka，偏移了1.9 m，而1.12 ka的阶地T3位移了1.11 m。T3阶地的年龄和错距结合断层倾角为1.25 °，确定Peñas断层的缩短速率为1.2.0 mm/a，即，大约是现在在前心脏地带东部边缘缩短的一半。在Cal断层，阶地T2至T4的年龄分别为0.8ka（OSL）、0.39ka（14 C）和≤12 ka（10 Be），垂直偏移分别为0.26m、0.36m和0.70m，这意味着断层上的滑动最近有所加速。因此，卡尔断层对门多萨的一百万居民构成了严重的地震危险。
During the last few hundred years several destructive earthquakes occurred along the eastern margin of the Andean Precordillera, where GPS data reveal a shortening rate of ∼4.5 mm/a. We use fault scarp profiles and age determinations of deformed terraces (T1–T4) to infer coseismic displacements and quantify slip rates for the Peñas and Cal thrust faults near Mendoza city. Scarps on the lowest terrace level T1 reveal vertical offsets of 0.8–1.0 m for both faults, which are interpreted as coseismic displacements during the last earthquake. Together with the fault dip these offsets indicate that both faults are capable of producing magnitude MW ∼6.9 earthquakes, which is corroborated by a magnitude MS = 7.0 event on the Cal fault that destroyed Mendoza in 1861. At the Peñas thrust fault, terrace T2 has an age of ∼3.3 ka and is offset by ∼1.9 m, whereas the ∼12‐ka‐old terrace T3 is displaced by ∼11 m. Combined with the fault dip of ∼25°, the age and offset of terrace T3 define a shortening rate of ∼2.0 mm/a on the Peñas fault, i.e., about half of the present‐day shortening at the eastern margin of the Precordillera. At the Cal fault, terraces T2 to T4 have ages of ∼0.8 ka (OSL), ∼3.9 ka (14C), and ≤12 ka (10Be) and are vertically offset by ∼2.6, ∼3.6, and ∼7.0 m, respectively, which implies that slip on the fault has recently accelerated. Hence, the Cal fault poses a serious seismic hazard to the one million inhabitants of Mendoza.